Antiflammable Properties of Capable PhosphorusâNitrogen

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Chapter 9

Antiflammable Properties of Capable Phosphorus−Nitrogen-Containing Triazine Derivatives on Cotton SeChin Chang,* Brian Condon, Thach-Mien Nguyen, Elena Graves, and Jade Smith Southern Regional Research Center (SRRC), United States Department of Agriculture (USDA) – Agricultural Research Service (ARS), 1100 Robert E. Lee Blvd., New Orleans, Louisiana 70124 *E-mail: [email protected]

Herein we present the synthesis and application of triazine derivatives as flame retardants on cotton. Novel phosphorus−nitrogen-containing compounds (TPN1, TPN2, TPN3 and TPN4) were prepared by organic reactions of cyanuric chloride and phosphonates. They were characterized by analytical tools such as proton (1H) and carbon (13C) nuclear magnetic resonance (NMR) spectroscopy, and elemental analysis (EA). Cotton twill fabrics were soaked in 10-20% aqueous sodium hydroxide and then treated with TPN1-TPN4 in various organic solvent mixtures. The compounds were grafted onto the fabric by traditional pad, dry, cure methods to produce semi-durable flame resistance. Thermogravimetric analysis (TGA) provided degradation and char content information on all materials by measuring the change in mass as a function of rising temperature. Treated fabrics were evaluated for flame resistance by such methods as vertical flammability test (ASTM D6413-08), 45° angle flammability test (ASTM D1230-01) and limiting oxygen index (LOI, ASTM D2863-09).

Not subject to U.S. Copyright. Published 2012 by American Chemical Society In Fire and Polymers VI: New Advances in Flame Retardant Chemistry and Science; Morgan, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2012.


Introduction In response to increasing government regulation for fire safety and environmental issues, new flame retardants such as non-halogenated, non-toxic, and environmentally friendly materials are needed (1). Phosphorus-containing compounds are widely used in the textile industry to make cotton textiles flame resistant (2, 3). Phosphorus-containing flame retardant compounds have been chemically reacted with cotton, producing products with an ether cross linker between the phosphorus compound and the cellulosic material. In the condensed phase, the phosphorus-containing functional groups are converted by thermal decomposition to phosphoric acid, forming a protective char. Char development and intumescence provide low flammability to cotton textiles (4, 5). Nitrogen-containing flame retardants, in combination with phosphorus compounds, have multifunctional advantages: 1) low toxicity during combustion, 2) high efficiency as measured by cone calorimetry, and 3) low smoke development in fire accidents (6). Some nitrogen-containing compounds, such as urea, dicyandiamide, and melamine, will accelerate phosphorylation of cellulose through formation of a phosphorus-nitrogen intermediate, and thus synergize the flame retardant action of phosphorus (7, 8). Triazine and its derivatives are known as flame retardant materials and good charring agents because of their abundant nitrogen and structure of tertiary nitrogen (9). Furthermore, triazines are of beneficial merit since they are commercially available, comparatively cheap, and environmentally clean materials. This research is focused on an organophosphorus flame retardant. Monoand di-substituted diethyl phosphonate (TPN1 and TPN2) and dimethyl hydroxymethylphosphonate (TPN3 and TPN4) derivatives of cyanuric chloride were chosen as potential flame retardants for cotton. The choice of cyanuric chloride is based on its affordability and the advantage of its chemical structure, with abundant nitrogen. Utilizing the existing dye and flame retardant chemistry between cyanuric chloride and cotton (10–13), cyanuric chloride was derivatized with phosphonate. This article presents the preparation of TPN1-TPN4, and the comparison of the synthesis and characterization, flame retardant performance, including vertical and 45° angle flammability and LOI testing, as well as thermal properties by thermogravimetric analysis (TGA) of the flame retardant treatments on cotton twill fabric.

Experimental Materials and Measurements Some of the synthesis and characterization of the flame retardants covered in this paper were as reported (14, 15). Triethylphosphite, dimethylphosphate, paraformaldehyde, potassium carbonate, and cyanuric chloride were purchased from Sigma-Aldrich. Regent grade solvents and all other commercially available reagents were used as received. All reactions were carried out under nitrogen atmospheric conditions and monitored using silica gel 60 F254 thin layer 124 In Fire and Polymers VI: New Advances in Flame Retardant Chemistry and Science; Morgan, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2012.


chromatography (TLC) purchased from EMD. Twill fabric, 258g/m2 (Testfabrics, Inc., Style 423) was bleached and mercerized. 1H and 13C NMR spectra were recorded on a Varian Unity plus 400 spectrometer (400 MHz) at ambient probe temperature. Tetramethylsilane and CDCl3 were used as internal reference. GC/MS was carried out on an Agilent 6890GC coupled to a time-of-flight mass spectrometer (Leco Corporation, St. Joseph, MI) with a DB-5 (Supelco, Bellefonte, PA) capillary column of 30 m x 0.25 mm ID x 0.25 µm as stationary phase. Elemental analyses were carried out on a 2400 series II CHNS/O Analyser, PerkinElmer and ICP Leeman Labs Prodigy/Prism at 253 and 561 nm. Synthesis of Diethyl 4,6-dichloro-1,3,5-triazin-2-ylphosphonate, TPN1 A mixture of cyanuric chloride (20.0 g, 110 mmol) and anhydrous toluene (250 mL) were stirred at room temperature until dissolved, and then this solution was stirred 1 hour at 0°C. To this solution, triethylphosphite (21.6 g, 130 mmol) in anhydrous toluene (100 mL) was added dropwise at 0°C. When the addition was complete, the reaction mixture was cooled to 0°C for 7-8 hours, then allowed to warm to room temperature and stirred overnight. The solvent was removed via rotary evaporation and a light yellow oil was obtained (32.0g, 86.0% yield). 1H NMR (400MHz, CDCl3) δ-ppm: 1.46 (t, 6H, POCH2CH3), 4.45 (q, 4H, POCH2CH3). 13C NMR (100MHz, CDCl3) δ-ppm: 16.4, 65.5, 172.3-176.7. m/z observed 286.0 (calcd. 286.05). Anal. Calcd for C7H10Cl2N3O3P: C=29.39%; H=3.52%; N=14.69%. Found C=30.02%; H=5.50%; N= 11.18%. Synthesis of Tetraethyl 6-chloro-1,3,5-triazin-2,4-diyldiphosphonate, TPN2 Cyanuric chloride (19.9 g, 0.11 moles) in anhydrous toluene (400ml) was stirred for 1 hour with gentle heating to a temperature of approximately 60°C. A solution of triethylphosphite (37.7 g, 0.23 moles) in anhydrous toluene (200 ml) was added dropwise over 1 hour under nitrogen atmosphere with increased heating to 90°C. The mixture was refluxed for 18 hours and the solvent was evaporated after filtration. A light yellow oil was obtained (40.7 g, 98.0 % yield). 1H NMR (400 MHz, CDCl3): δ 1.33 (t, 12H, POCH2CH3), 4.32 (q, 8H, POCH2CH3). 13C NMR (100 MHz, CDCl3): δ 16.1, 65.0, 170.6-175.2. M+Na observed 410.05 (calcd 387.69). Anal calcd for C11H20ClN3 O6P2: C=34.04%; H=5.20; N=10.84; Found C=30.02%; H=5.50; N=11.18 %. Synthesis of Dimethyl (4,6-dichloro-1,3,5-triazin-2-yloxy)methyl Phosphonate, TPN3 A mixture of cyanuric chloride (5.0 g, 27 mmol) and acetone (170 mL) was stirred at room temperature until dissolved. The solution was then cooled to 0°C. To this solution, dimethyl hydroxymethyl phosphonate (3.80 g, 27 mmol) in H2O (100 mL) was added dropwise. The pH of the reaction mixture was adjusted to 5.5-6 with solid anhydrous K2CO3 as needed throughout the experiment. The reaction progress was followed by TLC using 5% MeOH/EtOAc as eluent. When the addition was complete, the ice bath was removed, and the reaction was allowed 125 In Fire and Polymers VI: New Advances in Flame Retardant Chemistry and Science; Morgan, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2012.


to warm to room temperature. After fifteen minutes at room temperature, TLC confirmed the disappearance of cyanuric chloride and the appearance of the desired product. The solid was then filtered off, and the acetone was removed via rotary evaporator. Brine (100 mL) was added, and the solution was extracted with CHCl3 (3 x 200 mL). The organic layer was combined, dried over Na2SO4, filtered and evaporated to obtain a colorless oily compound. This was further dried under high vacuum to give an off-white solid at 75-80 % yield. 1H NMR (400MHz, CDCl3) δ-ppm: 3.86 (d, 6H, POCH3), 4.80 (d, 2H, -OCH2P). 13C NMR (100MHz, CDCl3) δ-ppm: 53.6, 60.5, 171.0, 173.0. 31P NMR (162MHz, CDCl3) δ-ppm: 18.8 (m). m/z observed 288.0 (calcd. 288.03). Anal. Calcd for C9H16ClN3O8P2: C= 25.02%; H= 2.80%; N= 14.60%; P= 10.75%. Found C= 25.27%; H= 2.91%; N= 14.72%; P= 10.71%. Synthesis of Tetramethyl (6‐‐chloro‐‐1,3,5‐‐triazine‐‐2,4‐‐diyl)bis(oxy)bis(methylene) Diphosphonate, TPN4 A mixture of cyanuric chloride (2.0 g, 10.85 mmol) and acetone (70 ml) was stirred until dissolved. To this solution, dimethyl hydroxymethyl phosphonate (3.36 g, 24 mmol) was added dropwise. The solution was then cooled to 0°C. A mixture of aqueous 50% w/w NaOH in 30 ml of distilled water was added dropwise to the above solution. The reaction was allowed to warm to room temperature after 2 hours and was monitored by the Fujiwara test (19) and TLC with MeOH/EtOAc as an eluent. After the solvent was removed via rotary evaporation, the aqueous solution was then extracted with CHCl3. The organic layer was combined, dried over Na2SO4, filtered, and evaporated to obtain a colorless oily compound. This was further dried under high vacuum to give a white solid at 76–82% yield. 1H NMR (400 MHz, CDCl3) δ (ppm): 3.85 (d, 12H, POCH3), 4.80 (d, 4H, -OCH2P). 13C NMR (100 MHz, CDCl3) δ (ppm): 53.5, 60.0, 172.0, 173.2. 31P NMR (162 MHz, CDCl3) δ (ppm): 19.9 (septet). m/z observed 392.0 (calcd. 391.64). Anal. calcd. for C9H16ClN3O8P2: C = 27.60%; H = 4.12%; N = 10.73%; P = 15.82%. Found C = 26.70%; H = 4.21%; N= 10.23%; P = 16.10%. Fabric Treatment The fabric used was cotton twill (238 g/m2) that was desized, scoured, bleached and mercerized. Fabric samples (17 x 9 in.) were soaked in a 20 % sodium hydroxide solution for 2 hours and processed on a two roll padder at 40 psi pressure. The cotton fabric was then treated with 50% aqueous isopropanol formulations containing various percentages of TPN1-TPN4. Fabric samples were immersed in the treatment solution overnight for thorough wetting, then padded (10 psi), dried (100°C, for 5 min), and cured in air (140°C, for 5 min). After curing, the fabric was allowed to cool to room temperature. Weight of the fabric before and after treatment was recorded. The wet pick-up weight after padding and the dry pick-up weight after drying in the dessicator were obtained. Flammability testing was carried out immediately after obtaining the add-on value. 126 In Fire and Polymers VI: New Advances in Flame Retardant Chemistry and Science; Morgan, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2012.

Limiting Oxygen Index (LOI) and Flammability Test (Vertical and 45° Angle)


The limiting oxygen index (LOI) values were measured on a limiting oxygen index chamber (Dynisco polymer test) with strips of fabrics (6.35×12.7 cm) according to ASTM D-2863-09 (16). Vertical flame tests were conducted on a vertical flammability model VC-2 instrument (Govmark Inc.) with strips of fabrics (30×7.6 cm) according to ASTM D-6413-08 (17). 45° angle flame tests were performed on strips of fabric (15 x 6 cm) according to ASTM D-1230-01 (18). Thermogravimetric Analysis (TGA) Onsets of degradation (20–22) and char content at 600°C were obtained from thermogravimetric analysis (TGA) thermograms. Fabric degradations were observed for untreated and treated fabrics in nitrogen atmosphere by TGA (from 20 to 600°C, heating rate 10°C/min).

Results and Discussion Synthesis and Characterization of Flame Retardants, TPN1-TPN4 Diethyl 4,6-dichloro-1,3,5-triazin-2-ylphosphonate, TPN1, and tetraethyl 6-chloro-1,3,5-triazin-2,4-diyldiphosphonate, TPN2, were prepared in one step as shown in Scheme 1. TPN1 was synthesized by cyanuric chloride and triethylphosphite in anhydrous toluene at 0°C. Following work up, TPN1, was obtained in 86.0% yield as a light yellow oil. It afforded baseline 1H and 13C NMR spectra and needed no further purification. Tetraethyl 6-chloro-1,3,5-triazine-2,4-diyldiphosphonate, TPN2, was also prepared in one step through the Michaelis-Arbrusov reaction followed by oxidation of cyanuric chloride and triethylphosphite in toluene at reflux condition as light yellow oil (98.0 % yield) (14). 1H and 13C data for TPN1 and TPN2 are consistent with structure as explained in Table I. In Figure 1(a) 1H NMR spectrum of TPN1, the chemical shift at 4.48-4.40 ppm belongs to the -OCH2CH3 protons and the chemical shift at 1.48-1.35 ppm are assigned to the -OCH2CH3 protons. Figure 1(b) shows the 13C NMR spectrum of TPN1. The peak at about 16.4 and 65.5 ppm are assigned to -OCH2CH3 and -OCH2CH3. Also, the peaks at about 171.0-177.0 ppm belong to aromatic back bond carbons. Synthesis and characterization of TPN2 was reported earlier, and most of the chemical shifts of NMR data had very similar values to TPN1 (14). Dimethyl(4,6-dichloro-1,3,5-triazin-2-yloxy)methyl-phosphonate, TPN3, and tetramethyl (6‐chloro‐1,3,5‐triazine‐2,4‐diyl)bis(oxy)bis(methylene) diphosphonate, TPN4 (15), were successfully synthesized in one simple step in high yield of 75-82% (Scheme 1). The product could be used without further purification. TPN3 readily dissolved in MeOH, THF, acetone, and chloroform. It dissolved slowly in ethyl acetate and methylene chloride. Like TPN4 (15), the temperature, pH of reaction medium, and molar ratio between cyanuric chloride 127 In Fire and Polymers VI: New Advances in Flame Retardant Chemistry and Science; Morgan, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2012.


and dimethyl hydroxylmethyl phosphonate were important factors in preparation of TPN3. TPN3 formation favored low temperature and slightly acidic medium, while TPN4 could be obtained at room temperature and in slightly basic medium. The chemical structure of TPN3 was studied by NMR, GC-MS, and elemental analysis. Chemical shift of NMR results for TPN3 and TPN4 are listed in Table I for comparison. Both compounds have 2 signals in 1H NMR data and 4 signals in 13C NMR data. Figure 1(c) shown 1H NMR of TPN3. The six protons at 3.87 ppm and two protons at 4.84 ppm, are assigned to methoxy and methylene protons, respectively. Figure 1(d) showed 4 signals of carbon. The peak at about 53.6 and 61.3 ppm are assigned to -OCH3 and -OCH2POCH3, respectively. Also, the peaks at about 171.0 and 173.0 ppm belong to the aromatic back bond carbons. From Table I, it is obvious that the chemical shifts in proton and carbon data of two compounds are close to each other. It is noticeable that the carbon which attaches to oxygen of phosphorus group (C-O) appears as a doublet. When comparing peak amplitude for this carbon and the carbon attaches to chlorine (C-Cl), it is obvious that both types of carbon exhibit the same amplitude in TPN4, but the C-O amplitude is intensively reduced in TPN3. This may due to the substituent’s type and the number of the substituent on the cyanuric ring. The GC-MS spectrum of TPN3 provided a molecular ion peak of product 288 and its isotope. The experimental values of elemental analysis are close to the calculated ones. These instrumental analyses results confirm that the chemical structure of TPN3 is the same as that proposed in Scheme 1.

Scheme 1. Synthesis of TPN1, TPN2, TPN3 and TPN4 128 In Fire and Polymers VI: New Advances in Flame Retardant Chemistry and Science; Morgan, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2012.

Fabric Treatment and Phosphorus and Nitrogen Contents


Cotton twill fabric was treated with solutions of TPN1-TPN4 (w/v in 50% aqueous isopropanol) at room temperature. The fabric was weighed before and after treatment and the data were fitted to equation 1 and 2 to obtain wet pick-up and add-on percents.

Table I. Chemical structure and NMR shift data for TPN1, TPN2, TPN3 and TPN4

Overall, TPN3 samples show more wet pick-up than TPN4 samples. Surprisingly, 10 wt% add-on of TPN3 achieved the same wet pick-up as 19 wt% add-on of TPN4. After curing, all TPN4 samples appeared off-white but samples treated with TPN3 turned grey. In addition, TPN3 samples were stiffer and more brittle than TPN4 samples. 129 In Fire and Polymers VI: New Advances in Flame Retardant Chemistry and Science; Morgan, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2012.


Figure 1. 1H and 13C NMR spectra of TPN1(a:1H and b:13C) and TPN3(c:1H and d:13C). All add-on percents and their phosphorus and nitrogen percent results were summarized in Figure 2. Content of phosphorous and nitrogen for TPN1 and TPN2 were determined analytically for each add-on sample with three observations for nitrogen and six observations for phosphorous. It is apparent that the content of 130 In Fire and Polymers VI: New Advances in Flame Retardant Chemistry and Science; Morgan, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2012.


phosphorous and nitrogen increases with the increase of add-on value, and nitrogen content is always higher than phosphorous content in each sample. Nitrogen has been recognized to play a role in fire retardancy and adding nitrogen often reduces the need for phosphorous (23). The graphical P-N synergistic effect for a variety of phosphorus-nitrogen systems on cotton twill showed that P+N should be 3.5-6% for flame retardancy (24, 25).

Figure 2. Add-ons (wt %) and contents of phosphorus and nitrogen in treated fabric of TPN1 and TPN2.

Thermal Properties of Flame Retardant Treated Fabric The thermal degradation data were obtained in a nitrogen atmosphere. Degradation of untreated control twill and various add-ons (wt %) of treated twill samples with TPN1-TPN4 are presented graphically in Figure 3. Untreated twill fabric showed an onset temperature at 327°C and char residue of 3% of the original weight at 600°C. Treated twill fabric for TPN1 and TPN2 with 4-33 add-on (wt %) were degraded between 260 and 295°C, and provided char yield between 15 and 27%. In general, onsets of degradation of the TPN1 series are very similar to results with the TPN2 series. However, onsets of degradation of the TPN3 series are lower than that of the TPN4 series. Furthermore, the 131 In Fire and Polymers VI: New Advances in Flame Retardant Chemistry and Science; Morgan, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2012.


TPN3 series degrades at a lower temperature than TPN4 but provides higher char content at 600°C. 5 and 10 wt% add-on TPN3 samples show onset of degradation at 244 and 242°C; whereas, the onset of degradation of 5 and 9 wt% add-on TPN4 samples are 287 and 283°C. Within TPN3 and TPN4 indivially, these percent yield almost the same char content. Although TPN3 with 16 and 21 wt% add-ons and TPN4 with 14 and 19 wt% add-ons provide the same char content, 16 and 21 % samples display the same onset of degradation, while the onset temperature of 14 wt% add-on is higher than that of 19 wt% add-on. The onset temperature of the compound decreases with increasing concentration of the phosphorus moiety, while the onset temperature of the treated fabric decreases with decreasing concentration of phosphorous moiety.

Limiting Oxygen Index (LOI) and Flame Tests (Vertical and 45° Angle) of Fabrics

LOI values indicate the minimum amount of oxygen needed to sustain a candle-like flame when a sample is burned in an atmosphere of oxygen and nitrogen. Textiles are considered to be flammable when LOI values are below 21% oxygen in nitrogen and are considered to be flame retardant when LOI values fall in the range of 26–28%. At these LOI values, flame retarded test fabric samples are expected to pass open flame tests in either the 45° angle or vertical direction (26, 27). Passing an open flame test means that the ignited test sample self extinguished following a very short after-flame time, did not glow after the flame extinguished by itself, and showed a char length that did not equal the length of the test sample. LOI values and vertical flame tests of untreated fabrics and those treated with TPN1 and TPN2 are shown in Table II. LOI values of untreated fabrics were 18% oxygen in nitrogen. LOI data for treated fabrics ranged between 28 and 48%. TPN1 series provided LOI values of 28, 37, 45, 38 and 48% when add-on values were 4, 12, 17, 26 and 33 wt %. With the TPN2, LOI values were 28, 36, 42, 45 and 48% when add-on values were 4, 10, 15, 24 and 31 wt %. All samples treated with TPN1 and TPN2 have high LOI values. The lowest, 4 wt% add-on, and the highest, 33 wt% add-on, have LOI values of 28 and 48%, respectively. LOI value increases seem to reach a limiting value with respect to add-on which higher phosphorus content for improved flame resistance. Convinced that our new triazine based monomers will afford flame resistance to fabrics of different constructions, we tested the treated fabrics by the vertical flame test, ASTM D-6413-08 and observed satisfying results. Following 12-sec exposure to flame, treated fabric with more than 12 and 10 wt% add-on for TPN1 and TPN2 samples, respectively showed no observable after-flame and after-glow times, and char lengths were less than 6-8.5cm. Based on vertical flammability and LOI results, it can be concluded that TPN1 and TPN2 act as good flame retardants when applied to cotton twill fabrics at a level of 10 wt% add on or higher. The results are particularly useful for textile articles of commerce protected under 16CFR Parts 1610.17 132 In Fire and Polymers VI: New Advances in Flame Retardant Chemistry and Science; Morgan, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2012.


Figure 3. Degradation thermograms of TPN1, TPN2 (14), TPN3, and TPN4 (15) treated fabrics at various add-ons (wt %) by TGA in nitrogen atmosphere.

To evaluate the flame retardancy of TPN3 and TPN4, treated samples with different add-on values were selected for modified standard 45° angle flammability and standard limiting oxygen index testing. Standard 45° angle flammability test (18) establishes flammability requirements that all clothing textiles, as defined in the Standard for the Flammability of Clothing Textiles, must meet before sale or introduction into commerce. The Standard provides a method for testing and establishes three classes of flammability performance of textiles and textile products used for clothing, thereby restricting the use of any dangerously flammable clothing textiles. In this test procedure, a 16 mm (5/8 in) flame impinges on a specimen mounted at a 45° angle for 10 second. The specimen is allowed to burn its full length or until the stop thread is broken, a distance of 127 mm (5 in). Samples of class I or II meet the requirements of the Standard. If the sample is assigned as class III, rapid and intense burning, it fails to meet the requirements of the Standard. The results of LOI and 45° angle flammability test results for samples treated with TPN3 and TPN4 are presented in Table III (28). 133 In Fire and Polymers VI: New Advances in Flame Retardant Chemistry and Science; Morgan, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2012.


Table II. Vertical flammability (ASTM D-6413-08) (17) and limiting oxygen index (LOI) (ASTM D-2863-09) (16) test for different add-ons (wt %) of treated twill fabrics for TPN1 and TPN2. [σ]= standard deviation

From Table III, it is seen that TPN4 with 14 and 19 wt% add-ons TPN4 and all TPN3 samples did not exhibit ignition after removal of the flame. Although obtaining the same add-on, 5 wt% add-on TPN4 had 80 seconds of flame spread and 35 seconds of glowing, while 5 wt% add-on TPN3 did not display ignition or glowing. The TPN4 sample with 9 wt% add-on had 46 seconds of flame spread and went out but 10 wt% add-on TPN3 did not exhibit ignition. Based on the Standard, at a concentration of 5 wt% add-on or higher of TPN3 or TPN4, treated fabric can be designated class 1 textile. 134 In Fire and Polymers VI: New Advances in Flame Retardant Chemistry and Science; Morgan, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2012.


Table III. 45° angle flammability (ASTM D-1230-01) (18) and limiting oxygen index (LOI) (ASTM D-2863-09) (16) test for different add-ons (wt %) of treated twill fabrics for TPN3 and TPN4 (28). [σ]= standard deviation

All samples treated with TPN3 had high LOI values. The lowest, 5 wt% addon, and the highest, 21 wt% add-on, had LOI values of 30 and 40%, respectively. TPN4 samples had high LOI value of 31 and 36% only at high add-on levels of 14 and 19 wt%, respectively. It has been established (29) that materials with LOI values in the range of 20.95 to 28% are known as slow burning. Above this range, materials are considered to be self-extinguishing. As a result of the LOI experiment, TPN3 can be classified as a flame retardant even at low add-on values.

Conclusions A new derivative of triazine based phosphorus–nitrogen containing monomers, TPN1, TPN2, TPN3 and TPN4, were successfully synthesized and characterized. All monomers were prepared in high yield 75-98%. Their flame resistant properties on cotton twill fabric were compared. TGA results showed that all treated fabrics were degraded at much lower temperatures and produced higher char yields at 600°C in nitrogen compared to that of untreated fabrics. In flammability test, such as LOI, 45° angle, and vertical test, most of treated fabrics with triazine based monomers were acceptable for their flame resistance performance. 135 In Fire and Polymers VI: New Advances in Flame Retardant Chemistry and Science; Morgan, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2012.


Fabric treated with TPN1 and TPN2 showd very similar results for onset of degradation, LOI values and char contents. Moreover, fabric treated with TPN3 exhibited lower onset of degradation than fabric treated with TPN4, and low add-on TPN3 samples obtained higher char content than TPN4 samples. In conclusion, these four monomers of triazine based phosphorus−nitrogen-containing derivatives are promising flame retardants for applications to cotton fabric. In the future, pyrolysis mechanism will be investigated to understand their flame retardant pathway.

Acknowledgments The authors wish to acknowledge the USDA-ARS CRIS for financial support. We also appreciate the skillful experimental assistance of Dr. Minori Uchimiya, Linda Wartelle, and Christa Madison.

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